In order to ensure that electronic signals or waveforms traveling along different paths arrive to the destination at a predetermined time, propagation delay techniques are used. To delay signal propagation, time delay circuits are preferred over increases in transmission line length for the delay purposes. In radar systems, time delay circuits can be used in conjunction with transmission lines to control beam steering in an active array radar system. The active array radar systems, or active electronically scanned arrays (AESA), are used to identify the range, altitude, direction, geometry or speed of both moving and fixed objects such as aircraft, ships, people, motor vehicles, weather formations, and terrain.
Conventional time delay circuits for transmission lines can consume considerable layout space and lack an ability to adjust delay. For example, increasing the length of a transmission line adds time delay, but often requires additional layout space that could be used for other purposes. Slow wave structures, which might require less layout space, have also been proposed for delaying signals traveling along transmission lines. U.S. Pat. No. 6,950,590, the entire content of which is expressly incorporated herein by reference, describes a conventional slow wave structure. The slow wave structure is typically implemented by placing floating strips of metal beneath a transmission line. The floating strips of metal beneath the transmission line act as periodic parasitic capacitance loads to the transmission line. U.S. Pat. No. 7,332,983 to Larson, the entire content of which is expressly incorporated herein by reference, describes a tunable delay line that selectively grounds one or more floating strips. However, the delay line of Larson requires manual tuning using a jumper or other connector. Therefore, a system providing dynamic control of time delay along a transmission line is desirable.